The genus Coelomomyces is a large group of aquatic parasitic fungi that attack mosquito larvae and are capable of causing epizootics that result in larval mortalities in excess of 90 percent under field conditions. Members of the genus have been reported attacking all important genera of vector mosquitoes including vectors of malaria, yellow fever, and filariasis such as, respectively, Anopheles gambiae, Aedes aegypti, and Culex quinquefasciatus. Although the life cycle of Coelomomyces is now known and several species can be maintained in the laboratory in vivo for experimental studies, virtually nothing is known about the complex nutritional, physiological and environmental factors that favor reproduction of these fungi and the development of epizootics in the field. Moreover, media for in vitro culture of Coelomomyces have not been developed. The overall objective of this research is to evaluate the biological control potential of selected species Coelomomyces and determine how these fungi might be used in vector control programs. Employing Coelomomyces dodgei/Acanthocyclops vernalis/Anopheles quadrimaculatus as a model system, the more immediate objectives of the proposed research are to increase our understanding of the factors that control growth and reproduction of Coelomomyces fungi through attainment of the following specific aims: (1) determination of how photoperiod controls gametophyte differentiation and gamete release; (2) determination of the factors responsible for the significant increases in larval size, weight and longevity, and concomitant production of fungal sporangia; (3) determination of the effect of important environmental variables such as temperature, pH, and ionic concentration on fungal life stages; and (4) development of a medium for culturing these fungi in vitro. To achieve these aims, studies will focus on C. dodgei, and where appropriate, C. punctatus. The effect of photoperiod on gametogenesis will be determined by exposing developing gametophytes to series of light/dark regimes in which the length and onset of the light and dark periods are varied. Factors which affect sporophyte growth will be determined by analysis of larval hemolymph with emphasis on Juvenile Hormone levels. The effect of environmental variables will be determined by bioassay using meiospores, gametes and mosquito-infective zygotes. For in vitro studies, sporophytes or gametophytes will be grown in experimental media. The results of these studies will contribute to an assessment of the role Coelomomyces fungi may play in mosquito control.